1. Field of the Invention
Embodiments of the present invention relate to a method for manufacturing integrated circuit devices. More particularly, embodiments of the invention relate to forming stoichiometric tungsten nitride films using cyclic or atomic layer deposition.
2. Description of the Related Art
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago and are continually decreasing in size today. Metal gates made of tungsten are becoming important because of the resistance requirements of these smaller devices. Tungsten is a desirable material because it is widely available and has a lower resistivity and lower contact resistance compared to other conductive metals.
One drawback to using tungsten in a metal gate, however, is that a barrier layer is typically required between silicon and the tungsten to prevent the formation of tungsten silicide. Tungsten silicide has a higher resistivity than tungsten and thus, increases the overall resistance of the gate. Barrier layers, however, also increase the resistance of the device and are deposited in amounts greater than needed due to the inherent limitations of conventional deposition techniques.
Bulk deposition processes, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), are conventionally used to deposit barrier layers. Bulk deposition processes are high deposition rate processes that maintain certain deposition conditions for a period of time to deposit material having a desired thickness, typically greater than 1,000 angstroms. This time period varies depending on the dynamics of the reaction and can be complicated where a reaction condition must be maintained for a brief period of time in order to deposit a controllable and repeatable thin layer of material.
There is a need, therefore, for new methods for depositing controllable, repeatable, and thin barrier layers.